1. Field of the Invention
The invention generally relates to an optical device, in particular, to a zoom lens.
2. Description of Related Art
It is necessary for a projection apparatus to have a high luminance, high resolution and high zoom ratio. Known projection apparatus are generally configured to use a light valve such as liquid crystal display or digital micro-mirror device so as to project an image on the basis of the light valve on a screen surface through a zoom lens in an enlarged scale. Therefore, the projector is desired to project a large and bright projection image with high resolution in order to ensure appropriate visibility when the image is projected in an enlarged scale, and the scale of the projection image is depended on the zoom ratio of the zoom lens.
In order to provided an enlarged image with high luminance, known zoom lens of a projector apparatus may include multiple lens units of the zoom lens or arrange large quantity of lenses near the magnification side of the zoom lens. During a zooming process, a distance between lens groups of the zoom lens is adjusted and a distance between an image source and plurality of lens groups is increased. Therefore, the distribution of weight of the lenses is concentrate on the front part of the zoom lens during zooming. Tilting of the zoom lens might happen, and especially the zoom lens is adjusted to the telephoto end wherein the tilting is one of the main causes of dislocation of the enlarged image.
The information disclosed in Description of Related Art is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art. Further, the information disclosed in Description of Related Art does not mean that one or more problems to be resolved by one or more embodiments of the invention was acknowledged by a person of ordinary skill in the art.